1. Field of the Invention
The present invention relates to solid material fabrication. More specifically, the present invention relates to solid freeform fabrication through feedstock deposition using an energy beam and advancing a molten puddle of rapidly solidifying material layered upon a mold or base structure.
2. Description of the Related Art
Metal and composite part fabrication and utilization permeates modern industry. An enormous range of products incorporate such parts, which may range in size from tiny components to major structural elements of huge machines. Industry has developed a wide range of fabrication techniques for such parts, which address materials, costs, development time, and economies of production. Among these fabrication techniques are casting, forging, machining, stamping, assemblies, and additive manufacturing.
The casting process essentially consists of making a shaped mold, and then pouring or injecting liquid material into the mold followed by relatively slow cooling of the entire mold with the desired part solidifying therein. As compared to other part fabrication techniques casting typically yields weaker parts due to the affects of cooling, which causes the material microstructure to be less dense. Pores and voids within the part are also problematic to this process since the process can introduce pockets of gas bubbles into the casting. Casting is sometimes used for more complex part geometries where strength is not the highest priority. Castings are also limited by the choices of materials that may be cast due to cooling rate issues. The trend in casting technology is to utilize investment casting where the initial mold is destroyed during the creation of the part. This allows much more complex or unitized parts to be built, however, cost increases as compared to reusable molds because the mold must be recreated for each part produced.
The forging process today is essentially unchanged from the ancient art of blacksmithing. A metal material is heated until it becomes pliable, and then force is exerted on the material using a tool. Modern forges can produce a great deal of force. The forging process is limited to relatively non-complex parts. Part overhang areas, closed regions, and complex vertical surfaces cannot be fabricated using the forging process. Although there have been advances in controlling the temperature of the stock material and advances in using shaped tools, tremendous amounts of energy are required to bring a large billet to temperature before a forging tool can shape it. A forging operation generally requires a large capital investment and long lead times for tool fabrication. Additionally, creating custom tools for closed die forging is expensive and once the tool is fabricated, it cannot be changed without considerable expense and delay.
The machining process is one of the largest segments in the manufacturing industry. With machining, essentially a block or raw materials is drilled, cut and milled to reveal the desired part within. Typically, rolled billet material is used as the raw stock in machining operations. Machining operations are time consuming and material consumption inefficient. For instance, some aerospace industry machined parts can begin as 1400 kilogram billets of material, which are machined to a final part having net weight of perhaps 45 kilograms. This yields a 30:1 scrap ratio. Recent improvements in the machining industry have focused on high-speed machining operations. This has improved the cost of machined parts, but the capital investment in purchasing new machines has kept supplier competition down and prices high. Issues with gouging and cutter longevity are problematic and are still being addressed in the industry.
Part fabrication by stamping operations and assemblies of plural stamped parts are heavily used in the aerospace and automotive sectors. This approach produces many smaller, thin, and relatively simple shapes that are be assembled together by welding or by using mechanical fasteners. Small assemblies are then combined into larger assemblies until the structure is complete. An aircraft fuselage and automobile chassis are examples of these assembly techniques. These are labor-intensive approaches that add weight and complexity due to redundant structure and fasteners. The current industry trend is to produce unitized structures where multiple parts are designed and fabricated as one part.
Additive manufacturing is a relatively recent development. For example, Aeromet Manufacturing, in Eden Prairie Minn., has developed a process it calls “Laser Additive Manufacturing.” This process applies a powdered feedstock that is melted into a molten puddle using laser energy. Powder is added and the laser directed to build a part up with multiple layers. Parts are built up on a base plate of the same material as the powder and can be built up to near net shape of the final part. As such, the amount of machining required is substantially less than billet-machined parts. Similarly, Optomec, Inc. of Albuquerque, N. Mex. has commercialized a process called “Laser Engineered Net Shape” that also uses a laser heat source and a powdered filler material. Prior art additive systems are limited in deposition rates to about 15 cm3 per hour. While these systems yield good results for small parts, the inefficient power consumption of laser power sources and low deposition rates make them impractical of larger part fabrication projects. With respect to scaling these processes, the upper limit is probably in the 500 cm3 per hour, or lower, range. Additive manufacturing has increased flexibility in part production, however, size is limited and finish machining operation carry many of the same limits as machined parts.
Certain systems and products require high quality parts that can be produced in relatively small quantities. In these arenas, design flexibility and short turn-around times are important. Complex parts are often required, which may include overhangs, cavities, bores, bosses, slots, complex curvatures, or other design subtleties. Exotic alloys are frequently employed, which are expensive as raw material and are difficult to machine. While the list of such applications is vast, here are a few example applications.
Aerospace Industry
Titanium and Aluminum Components
High Strength Complex Parts
Space Station or Deep Space Mission Applications
Lightweight Metal Alloy Innovations
Jet Engine Components
Missile Manufacturing
Automotive Industry
High Strength Aluminum Bodies
Prototype Engine Blocks
Auto Racing Industry
Oil and Gas Industry
Drill Bit Applications
Pumping Technology
Chemical Processing Industry
Corrosive Material Handling
Complex Shaped Manifolds, Fluid Handling Parts
Shipbuilding Industry
Propeller Development
Components Exposed to Harsh Environments
Military Hardware
High Temperature Gun Barrels
Light Weight Tank Armor
Complex Shaped Penetrating Bomb Casings
High Hardness Materials Used for Bunker-Buster Applications
Fléchette and Sabo Projectiles
Nuclear Industry
Exotic Materials Fabrication
Tool Making Industry
High Temperature, High Wear Applications
Medical Implants and Prosthetics
Thus it can be appreciated that there is a need in the art for a system and method of fabricating solid freeform parts having the qualities and advantages of casting, the strength of forgings, the flexibility of machining, and the raw material advantages of near net shape deposition techniques.